1. Field of the Invention
The present invention relates to a processing method for a wafer using low-permittivity insulating films (low-k films) as interlayer insulating films.
2. Description of the Related Art
In a semiconductor device fabrication process, a plurality of crossing division lines called streets are formed on the front side of a substantially disk-shaped semiconductor wafer such as a silicon wafer and a gallium arsenide wafer to thereby define a plurality of separate regions where a plurality of devices such as ICs and LSIs are respectively formed. After grinding the back side of such a semiconductor wafer by using a grinding apparatus to reduce the thickness of the wafer to a predetermined thickness, the semiconductor wafer is divided into a plurality of individual chips respectively corresponding to the plural devices by using a cutting apparatus or a laser processing apparatus. The chips thus obtained are widely used in various electrical equipment such as mobile phones and personal computers.
In general, a cutting apparatus called dicing saw is used as the cutting apparatus mentioned above. This cutting apparatus includes a cutting blade having a cutting edge having a thickness of 20 to 30 μm. The cutting edge is formed by bonding superabrasive grains such as diamond grains and CBN grains with metal or resin. The cutting blade is rotated at a high speed, e.g., 30000 rpm and lowered to cut into the semiconductor wafer, thereby cutting the semiconductor wafer. In each semiconductor device formed on the front side of the semiconductor wafer, a plurality of metal wiring layers are laminated for signal transmission, and these metal wiring layers are insulated from each other by interlayer insulating films formed mainly of SiO2. In recent years, the distance between the adjacent wiring layers has become smaller in association with finer structure, causing an increase in capacitance between the adjacent wiring layers. As a result, there arises a remarkable problem such that signal delay occurs to invite an increase in power consumption.
To reduce a parasitic capacitance between the metal wiring layers, SiO2 insulating films are mainly used as the interlayer insulating films for insulating the metal wiring layers in forming the devices (circuits) in the prior art. However, low-permittivity insulating films (low-k films) lower in permittivity than the SiO2 insulating films have recently been used as the interlayer insulating films. Examples of such low-permittivity insulating films having a permittivity (e.g., k=2.5 to 3.6) lower than the permittivity (k=4.1) of the SiO2 films include inorganic films of SiOC, SiLK, etc., organic films such as polymer films of polyimide, parylene, polytetrafluoroethylene, etc., and porous silica films of methyl containing polysiloxane etc.
In the case of cutting a laminated layer including such low-permittivity insulating films along the division lines by using a cutting blade, there arises a problem such that the laminated layer is peeled off because the low-permittivity insulating films are very brittle like mica. To solve this problem, Japanese Patent Laid-open No. 2005-064230 or Japanese Patent Laid-open No. 2005-142398 has proposed a semiconductor wafer processing method including the steps of preliminarily applying a laser beam to a semiconductor wafer along the division lines to remove the laminated layer along the division lines and next cutting the semiconductor wafer along the division lines by using a cutting blade to thereby divide the wafer into individual chips.